Method and apparatus for delivering radio frequency electromagnetic energy to cook foodstuff

ABSTRACT

A method and apparatus for delivering radio frequency electromagnetic energy to cook foodstuff in an enclosed cavity of a cooking device includes generating, with a small signal generating component, a radio frequency signal at a first power level, amplifying the radio frequency signal to a second power level greater than the first power level with a radio frequency amplification component, and feeding the amplified radio frequency signal to the enclosed cavity.

BACKGROUND OF THE INVENTION

Current microwave cooking appliances use powerful tubes to generatemicrowaves with nominal operating frequencies to heat food. Adisadvantage of using such powerful sources is a limited ability tocontrol emission of the microwaves. Solid state sources enablespecifying emissions that allow for a more controlled cooking appliance.Some solid state sourced microwave cooking appliance designs includedetermining a model of the cavity of the microwave, but do not allow forspecified cooking strategies regarding the food within the cavity. Thereis a need to improve control of the emissions using solid state sourcesto achieve better heating for specific food items and more efficientappliances.

SUMMARY OF THE INVENTION

In one aspect, a method of delivering radio frequency electromagneticenergy to an enclosed cavity of a heating device includes generating,with a small signal generating component, a radio frequency signal at afirst power level that is pulse width modulated at a predetermined dutycycle, amplifying the radio frequency signal to a second power levelgreater than the first power level with a radio frequency amplificationcomponent, and feeding the amplified radio frequency signal to theenclosed cavity. The first power level is based on the gain of the radiofrequency amplification component and the predetermined duty cycle isbased on a ratio of an output power level for a desired heating cycle ofoperation to the second power level.

In another aspect, an apparatus for delivering radio frequencyelectromagnetic energy to an enclosed cavity of a heating deviceincludes a cavity configured to hold an article to be heated, a smallsignal generator to generate a radio frequency signal at a first powerlevel that is pulse width modulated at a predetermined duty cycle, apower amplifier connected to the small single generator to amplify theradio frequency signal generated by the small signal generator to asecond power level greater than the first power level, a transmissionline between the power amplifier and the enclosed cavity to feed theamplified radio frequency signal from the power amplifier to theenclosed cavity, and a controller configured to set the first powerlevel based on the gain of the power amplifier and to set thepredetermined duty cycle based on a ratio of an output power level for adesired heating cycle of operation to the second power level.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic view of a cooking device in the embodiment of amicrowave heating apparatus, in accordance with various aspectsdescribed herein.

FIG. 2 is a schematic view of the microwave heating apparatus of FIG. 1,in accordance with various aspects described herein.

FIG. 3 is a schematic view of a microwave heating apparatus according toa second embodiment of the disclosure, in accordance with variousaspects described herein.

FIG. 4 is an example a flow chart diagram of delivering radio frequencyelectromagnetic energy to cook foodstuff, in accordance with variousaspects described herein.

DETAILED DESCRIPTION

FIG. 1 illustrates a cooking device, shown as a microwave appliance ormicrowave oven 10, having a housing 12 defining a cavity 14 into whichat least one food item, article, or “foodstuff” 16 (schematically shownas a box) to be heated or cooked can be placed or held. The microwaveoven 10 FIG. 1 is illustrated having an open cavity 14 for ease ofdepiction of the foodstuff 16, and embodiments of the disclosure caninclude microwaves 10 having an enclosed cavity 14, such as by way of apivotable, movable, or removable panel, such as a door.

The microwave oven 10 includes a power source 17 with an input rangepreferably ranging from less than 1 W to 250 W and at least onemicrowave generator 18, which is capable of generating a radio frequencyelectromagnetic energy field (hereafter, “energy field”), with anoperating frequency preferably ranging from 2.401 GHz to 2.48 GHz. In anexemplary embodiment, the microwave oven 10 can have two or moremicrowave generators 18, wherein each microwave generator 18 iselectrically coupled with the power source 17. Each microwave generator18 can include at least one antenna (not shown) adapted to provide theenergy field generated by the microwave generator 18, which is fed intothe cavity 14 by way of at least one feeding port 20 electricallycoupled with each microwave generator 18 by way of at least oneconductor or transmission line 21.

The microwave oven 10 can also include a control system 22,communicatively coupled with the microwave generators 18, the powersource 17, or a combination thereof, and programmed or configured tocontrol the generation of the energy field by the microwave generator18. For example, the control system 22 can operably control the poweroutput of the power source 17, the operation of the at least onemicrowave generator 18, or electromagnetic characteristics of thegenerated energy field, such as power level or frequency. In embodimentsof the disclosure wherein at least two microwave generators 18 areutilized, the control system 22 can further operably control the phaseof the at least two microwave generators 18 to alter the interferencepattern of the electromagnetic waves of the energy field.

During cooking or heating operations, the control system 22 of themicrowave oven 10 operates to control the generation of the energy fieldby the microwave generators 18 and to provide the energy field into thecavity 14 by way of the feeding ports 20. The energy field interactswith the foodstuff 16 to heat or cook the foodstuff 16. The illustratedembodiment of FIG. 1 is one non-limiting example of an embodiment of thedisclosure. Additional non-limiting embodiments of the disclosure caninclude additional or alternatively located components, including butnot limited to, the microwave generators 18, feeding ports 20, controlsystem 22, power source 17, or the like.

FIG. 2 illustrates a schematic view of the microwave oven 10. While onlyone microwave generator 18 is illustrated for brevity, embodiments ofthe disclosure can include a plurality of microwave generators 18operating in independently, as a common group with common respectiveoutputs, or in a cohesive fashion wherein the plurality of microwavegenerators 18 operate to collectively provide the energy field utilizedto heat or cook the foodstuff 16 in the cavity 14. As shown, themicrowave generator 18 can include a small signal generator 24configured to generate the radio frequency signal at a first powerlevel, and a radio frequency power amplifying component, such as a solidstate radio frequency signal amplifier 26. The control system 22 canalso include a processor 30 and memory 32. The control system 22 or theprocessor 30 can be configured to provide or supply a control signal 28,that is, an analog or digital communication signal, to the microwavegenerator 18 or the small signal generator 24.

The memory 32 can include random access memory (RAM), read-only memory(ROM), flash memory, or one or more different types of portableelectronic memory, such as discs, DVDs, CD-ROMs, etc., or any suitablecombination of these types of memory. The control system 22 can beoperably coupled with the memory 32 such that one of the control system22 and the memory 32 can include all or a portion of a computer programhaving an executable instruction set for controlling the operation ofthe aforementioned components, or a method of operating the same. Theprogram can include a computer program product that can includemachine-readable media for carrying or having machine-executableinstructions or data structures stored thereon. Such machine-readablemedia can be any available media, which can be accessed by a generalpurpose or special purpose computer or other machine with a processor.Generally, such a computer program can include routines, programs,objects, components, data structures, algorithms, etc., that have thetechnical effect of performing particular tasks or implement particularabstract data types.

Machine-executable instructions, associated data structures, andprograms represent examples of program code for executing the exchangeof information as disclosed herein. Machine-executable instructions caninclude, for example, instructions and data, which cause a generalpurpose computer, special purpose computer, control system 22, orspecial purpose processing machine to perform a certain function orgroup of functions. In implementation, the functions can be converted toa computer program comprising a set of executable instructions, whichcan be executed by the processor 30.

The control signal 28 can include a desired cooking signalrepresentative of a heating or cooking energy field desired for heatingor cooking the foodstuff 16. Embodiments of the control signal 28 canfurther include a desired cooking signal generated or selected, forexample from a database, executable instruction set executed by theprocessor 30, look up table stored in memory 32, or the like, based atleast partially on the foodstuff 16 to be heated or cooked. For example,a user can select from a variety of foodstuff 16 settings or values on auser interface for heating or cooking cycles of operation tailored to aparticular foodstuff 16. In this sense, embodiments of the disclosurecan include configurations wherein the control system 22 includes a userinterface. Examples of tailored cooking cycles of operation can include,but is not limited to, a “defrost” selection, “popcorn” selection,“reheat” selection, “vegetables” selection, or the like.

The control signal 28 can also include a desired cooking signalrepresentative of heating or cooking energy field characteristicsdesired for heating or cooking of the foodstuff 16. For example, theheating or cooking energy field characteristics of the control signal 28can include, but is not limited to, a first power level desired, asecond power level desired, a signal switching frequency, and the like.At least a subset of the aforementioned representative signals includedin or carried by the control signal 28 can be configured, selected, ordetermined based on the foodstuff 16 to be heating or cooked, such asfrom a user interface as explained above. In another non-limitingexample, at least a subset of the aforementioned representative signalscan be configured, selected, or determined based on the electricalefficiency or gain of the microwave generator 18, the small signalgenerator 24, the solid state amplifier 26, or a combination thereof.For instance, the subset of representative signals can be configured,selected, or determined based on operating the microwave 10 at a maximumelectrical efficiency, an electrical efficiency above an efficiencythreshold value, an electrical efficiency with an efficiency thresholdrange, at maximum output power, at maximum amplification stage gain, ora combination thereof.

Embodiments of the disclosure can include configurations wherein atleast a subset of the aforementioned representative signals included inor carried by the control signal 28, including the aforementionedembodiments, can further be configured, selected, or determined byexecutable software operated by the microwave oven 10, control system22, or processor 30, or from a look up table stored in memory 32 andaccessible by the control system 22 or processor 30. For example, themaximum electrical efficiency, maximum gain, efficiency threshold value,efficiency threshold range, or a combination thereof can includerespective predetermined values stored in memory 32, or can be derivedbased on executable software to determine, develop, compute such values.In yet another embodiment of the disclosure, at least a subset of theaforementioned representative signals included in or carried by thecontrol signal 28 can be configured, selected, or determined based onfeedback or sensed characteristics of the foodstuff 16. Such feedback orsensed characteristics can be observer, sensed, or measured by way of aplurality of sensors, including, but not limited to, an optical sensorsuch as a camera, a steam or temperature sensor, or the like.

The small signal generator 24 receives the control signal 28, and inresponse to the control signal 28 and included representative signals,generates a first radio frequency signal 34 at the first low powerlevel. As used herein, a “low” power level denotes a signal, power, orenergy level below the energy field level utilized to heat or cook thefoodstuff 16. In one embodiment of the disclosure, the small signalgenerator 24 can generate a first radio frequency signal 34 in responseto the control signal 28, wherein the first radio frequency signal 34is, for example, pulse width modulated at a predetermined switchingfrequency. In this example, the predetermined switching frequency isdefined, controlled, selected, or instructed by the signal switchingfrequency energy field characteristic of the control signal 28.Non-limiting embodiments of the disclosure can include wherein thepredetermined switching frequency is at least 20 KHz. It will beunderstood that the predetermined switching frequency can define oraffect the energy field generated by the microwave generator 18. Forexample, the predetermined switching frequency can include controlling,altering, or defining a duty cycle for the microwave generator 18, thesmall signal generator 24, or the solid state amplifier 26.

In another non-limiting embodiment of the disclosure the predeterminedswitching frequency can be related to electrical regulations orpractical power source 17 concerns regarding the predetermined switchingon and off of the power, including flickering, modulation, power surgesor deficiencies, and the like. It is understood that pulse widthmodulation signals can be configured to operably control, select, orlimit an amount of energy field supplied to the cavity 14. Anothernon-limiting embodiment, the first radio frequency signal 34 can includea first low power level of less than 1 Watt, such as 300 milliwatt.

In yet another embodiment of the disclosure, the first radio frequencysignal 34 can be selected or generated based on the expected,predetermined, estimated, or derived electrical efficiency or gain of atleast one of the microwave generator 18, the small signal generator 24,or the solid state amplifier 26. For instance, the first radio frequencysignal 34 can include a predetermined switching frequency based at leaston a ratio of an expected or estimated output power level of the energyfield generated by the microwave generator 18, for a desired heating orcooking cycle of operation.

The first radio frequency signal 34 can be provided to the solid stateamplifier 26. Solid state amplifiers 26 include the operably ability tobe tunable and coherent, that is precisely controllable to amplify aspecific signal, compared with a magnetron source that is not narrowband and not tunable (i.e. emits microwave signals at a changingfrequency over time that is not precisely selectable). The solid stateamplifier 26 can operably amplify the first radio frequency signal 34having the first low power level to a second radio frequency signal 36having a second high power level embodying the heating or cooking energyfield utilized to heat or cook the foodstuff 16. During amplification bythe solid state amplifier 26, the power level can be increased from thefirst low power level to the second high power level, and thepredetermined switching frequency can be unchanged, or can remainconstant through the power amplification process. One non-limitingembodiment of the second radio frequency signal 34 can include a secondhigh power level of greater than 50 or 100 Watts, such as 250 Watts. Thesecond high power level can also be described in terms of a gain, suchas a 32 dB gain. While a single solid state amplifier 26 is illustratedfor brevity, embodiments of the disclosure can include a plurality ofsolid state amplifiers 26, each amplifying a first radio frequencysignal 34. The final output power of the energy field, for example froma plurality of microwave generators 18 can include 1000 Watts or more.

The second radio frequency signal 36 can then be provided to the cavity14, for example, by way of the feeding ports 20, wherein the energyfield can interact with the foodstuff 16 to heat or cook the foodstuff16, as desired. As illustrated, the power source 17 can be electricallycoupled with the control system 22, the small signal generator 24, thesolid state amplifier 26, or a combination thereof, to operably supplypower to the respective components. The power supplied by the powersource 17 can be utilized by the respective components to, for example,generate the control signal 28 in the control system 22, generate thefirst radio frequency signal 34 in the small signal generator 24,amplify the first radio frequency signal 34 to the second radiofrequency signal 36 in the solid state amplifier 26, or a combinationthereof.

When foodstuff 16 is heated or cooked by operably utilizing such a highpredetermined switching frequency, the food acts similar to a lowpassfilter such that the measureable heating effect increases the cookingefficiency of the microwave. Additionally, the heating or cookingemployed by the above-described embodiments can result in a more uniformor even temperature rise of the foodstuff 16, compared with conventionalmicrowaves.

While the aforementioned description explains that the first radiofrequency signal 34 having the first low power level can be amplified tothe second radio frequency signal 36 having a second high power level,embodiments of the disclosure can be included wherein the control signal28 includes representative signals indicative of the estimated orexpected second radio frequency signal 36 or the estimated or expectedsecond high power level, and wherein the first radio frequency signal 34or the first low power level is determined or selected based on thesecond radio frequency signal 36 or second high power level. Forexample, the first radio frequency signal 34 or the first low powerlevel can be determined, selected, or generated by the small signalgenerator 24 (e.g. by the control system 22 or processor 30, asexplained herein, and received by way of the control signal 28) suchthat the first radio frequency signal 34 is amplified to the secondradio frequency signal 36, wherein the microwave generator 18 operatesat the maximum electrical efficiency or gain, above or higher than theelectrical efficiency threshold value, within the bounds of anefficiency threshold range, maximum output power, maximum gain, or acombination thereof.

The above-described embodiment is effective in increasing or maximizingthe electrical efficiency of the microwave generator 18 when theestimated or expected second radio frequency signal 36 or second highpower level is known, and the amplification or gain of the solid stateamplifier 26 is known to occur at a high or maximum electricalefficiency or gain. For instance, the solid state amplifier 26 can beselected such that the desired, known, or predetermined operableamplification for the microwave 10 or microwave generator 18 occurs inthe compression zone of the solid state device, for improved electricalperformance and efficiency.

As used herein, the “compression zone” or “gain compression” of thesolid state amplifier 26 is related to the nonlinearity of the transferfunction of a solid state amplifying device. Outside the range of thecompression zone, the nonlinearity of the gain becomes apparent, and theefficiency of the gain is reduced due to, for example, thermal limits orthermal efficiencies of the solid state device. Stated another way, whena solid state amplifier 26 amplifier an input signal to a gained outputsignal outside of the compression zone, an increase in input will not bematched by a proportional increase in output, reducing the effectiveefficiency of the solid state amplifier 26. The compression zone can bedetermined, predetermined, or defined based on the selected solid stateamplifier 26, and can include a “deep gain compression zone” relative toa “compression point,” that is, a zone of substantially lineramplification relative to a maximum electrical efficiency or gain pointof amplification, or a zone or range about the compression point, suchas plus or minus 3 dB about the compression point.

In this sense, embodiments of the disclosure can increase or maximizethe electrical efficiency or gain of the microwave generator 18 by thecontrol system 22 or processor 30 determining a desired second radiofrequency signal 36 for heating or cooking the foodstuff 16, andconfigure, select, or determine at least a subset of the aforementionedrepresentative signals included in or carried by the control signal 28such that the amplification of the first radio frequency signal 34generated by the small signal generator 24 occurs with maximumelectrical efficiency or gain (e.g. based on a efficiency value orefficiency range, including amplification operation within thecompression zone, deep gain compression zone, or substantially at ornear the compression point, as explained above) based on operating thesolid state amplifier 26 in a predetermined compression zone.

In embodiments wherein the efficiency is based on a maximum electricalefficiency or gain, the first radio frequency signal 34 can be selectedsuch that the solid state amplifier 26 amplifies the first radiofrequency signal 34 to the second radio frequency signal 36 with actualor estimated maximum electrical efficiency. In embodiments wherein theefficiency is based on an electrical efficiency above an efficiencythreshold value, the first radio frequency signal 34 can be selectedsuch that the solid state amplifier 26 amplifies the first radiofrequency signal 34 to the second radio frequency signal 36 with actualor estimated electrical efficiency greater than the efficiency thresholdvalue. In embodiments wherein the efficiency is based on an electricalefficiency threshold range, the first radio frequency signal 34 can beselected such that the solid state amplifier 26 amplifies the firstradio frequency signal 34 to the second radio frequency signal 36 withactual or estimated electrical efficiency within the bounds of theelectrical efficiency threshold range.

Alternatively, or in addition to the above-described embodiment,embodiments of the disclosure can include configurations wherein theamplification of the first radio frequency signal 34 by the solid stateamplifier 26 operates such that the first radio frequency signal 34 isamplified to the second radio frequency signal 36 such that the secondradio frequency signal 36 includes the maximum output power or maximumgain operable for the solid state amplifier 26. This embodiment caninclude operating the solid state amplifier 26 in a maximum output powerregion or a maximum gain region of the amplifier 26, compared with amaximum electrical efficiency, described herein.

The determination of electrical efficiency or gain can further accountfor the actual or expected duty cycle or predetermined switchingfrequency of the first or second radio frequency signal 34, 36 duringoperation. In yet another example embodiment of the disclosure thecontrol system 22 or processor 30 can select or define an expected dutycycle or predetermined switching frequency for the first or second radiofrequency signal 34, 36 to maximize the electrical efficiency or gain ofthe microwave generator 18, as explained herein.

FIG. 3 illustrates an alternative microwave 110 and microwave generator118 according to a second embodiment of the disclosure. Where the secondembodiment is similar to the first embodiment, like parts will beidentified with like numerals increased by 100, with it being understoodthat the description of the like parts of the first embodiment appliesto the second embodiment, unless otherwise noted. A difference betweenthe first embodiment and the second embodiment is that the microwave 110of the second embodiment can include at least one power sensor 140positioned or configured to measure, sense, or sample at least one ofthe power of the first radio frequency signal 34 or the second radiofrequency signal 36, and provide the measurement to the control system22 or processor 30. Embodiments of the power sensor 140 can include anysensor configured to sense power or a characteristic related to power,including but not limited to, a current sensor or a voltage sensor. Asshown, optional configurations of the second embodiment of thedisclosure can include respective power sensors 140 on each of the firstand second radio frequency signals 34, 36.

Sensing or measuring the power of at least the first or second radiofrequency signal 34, 36 can include determining a value indicative of orrelated to the power level of the respective signal, rather thandirectly sensing or measuring the power itself. The sensed or measuredvalues can be provided to additional components. For instance, the valuecan be provided to a control system 22 or processor 30, and the controlsystem 22 or processor 30 can perform processing on the value todetermine a power level of the respective signal or a characteristicrepresentative of said power level.

The second embodiment of the disclosure can utilize the at least onepower sensor 140 provide feedback to the control system 22 or processor30 of the actual power levels of at least the first or second radiofrequency signals 34, 36. The feedback can enable the control system 22or the processor 30 to, for example, estimate, calculate, or determinedthe compression zone of the solid state amplifier 26, or any other powerlevel useful in estimating or determining the electrical efficiency orgain of the microwave 110 or the microwave generator 118. In this sense,the control system 22 or processor 30 can determine the maximumelectrical efficiency or gain (as described above) based on the sensedpower from the at least one power sensor 140.

FIG. 4 illustrates a flow chart demonstrating a method 100 of deliveringradio frequency electromagnetic energy to cook foodstuff in an enclosedcavity of a cooking device, such as a microwave. The method 100 beginsby generating, with the small signal generator 24, a radio frequencysignal at a first power level that is pulse width modulated at apredetermined switching frequency at 102. Next, the method 100 amplifiesthe radio frequency signal to a second power level, greater than thefirst power level, with the solid state amplifier 26 at 104. Finally,the method 100 feeds the amplified radio frequency signal to theenclosed cavity 14 at 106, wherein the amplified radio frequency signaloperably heats or cooks the foodstuff 16 within the cavity 14. Thesequence depicted is for illustrative purposes only and is not meant tolimit the method 100 in any way as it is understood that the portions ofthe method can proceed in a different logical order, additional orintervening portions can be included, or described portions of themethod can be divided into multiple portions, or described portions ofthe method can be omitted without detracting from the described method.

Many other possible embodiments and configurations in addition to thatshown in the above figures are contemplated by the present disclosure.

The technical effect of the above described embodiments enable a methodand apparatus for delivering radio frequency electromagnetic energy tocook foodstuff in a cooking device, such as a microwave. One advantagethat can be realized in the above embodiments is that the abovedescribed embodiments have superior electrical operating efficiencycompared to conventional microwave systems. Additionally, by operatingthe energy field at the predetermined switching frequency, themeasurable heating effects on the foodstuff are consistent over the highefficiency cooking period. Compare this with the heating effects whilecooking foodstuff with a conventional microwave, wherein thesignificantly longer or slower switching periods (on the order ofseconds) produce measureable heating effects followed by a suddentemperature decrease as the energy field is shut down, producingundesirable cooking temperature oscillations. The aforementionedoscillations in cooking temperature reduce the effective cookingefficiency or performance of the microwave.

To the extent not already described, the different features andstructures of the various embodiments can be used in combination witheach other as desired. That one feature cannot be illustrated in all ofthe embodiments is not meant to be construed that it cannot be, but isdone for brevity of description. Thus, the various features of thedifferent embodiments can be mixed and matched as desired to form newembodiments, whether or not the new embodiments are expressly described.Moreover, while “a set of” or “a plurality of” various elements havebeen described, it will be understood that “a set” or “a plurality” caninclude any number of the respective elements, including only oneelement. Combinations or permutations of features described herein arecovered by this disclosure.

This written description uses examples to disclose embodiments of thedisclosure, including the best mode, and also to enable any personskilled in the art to practice embodiments of the disclosure, includingmaking and using any devices or systems and performing any incorporatedmethods. The patentable scope of the disclosure is defined by theclaims, and can include other examples that occur to those skilled inthe art. Such other examples are intended to be within the scope of theclaims if they have structural elements that do not differ from theliteral language of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

What is claimed is:
 1. A method of delivering radio frequencyelectromagnetic energy to an enclosed cavity of a heating device, themethod comprising: generating, with a small signal generating component,a radio frequency signal at a first power level that is pulse widthmodulated at a predetermined duty cycle; amplifying the radio frequencysignal to a second power level greater than the first power level with aradio frequency amplification component; and feeding the amplified radiofrequency signal to the enclosed cavity; wherein the first power levelis based on the gain of the radio frequency amplification component andthe predetermined duty cycle is based on a ratio of an output powerlevel for a desired heating cycle of operation to the second powerlevel.
 2. The method of claim 1 further comprising determining a maximumefficient range for the radio frequency amplification component.
 3. Themethod of claim 2 wherein the maximum efficient range is determined byone of sampling and measuring power output from the radio frequencyamplification component and retrieving data from a lookup table.
 4. Themethod of claim 2 wherein the first power level is selected to beamplified within the maximum efficient range.
 5. The method of claim 4wherein the first power level is selected to be amplified in a deep gaincompression zone relative to a compression of the radio frequencyamplification component.
 6. The method of claim 4 wherein the firstpower level is selected to be amplified in a deep gain compression zonerelative to at least one of a maximum efficiency or a maximum outputpower of the radio frequency amplification component.
 7. The method ofclaim 1 further comprising determining a maximum power needed to heat anarticle in the heating device, and setting the predetermined duty cyclebased on the maximum power needed.
 8. An apparatus for delivering radiofrequency electromagnetic energy to a heating device comprising: anenclosed cavity configured to hold an article to be heated; a smallsignal generator to generate a radio frequency signal at a first powerlevel that is pulse width modulated at a predetermined duty cycle; apower amplifier connected to the small single generator to amplify theradio frequency signal generated by the small signal generator to asecond power level greater than the first power level; a transmissionline between the power amplifier and the enclosed cavity to feed theamplified radio frequency signal from the power amplifier to theenclosed cavity; and a controller configured to set the first powerlevel based on the gain of the power amplifier and to set thepredetermined duty cycle based on a ratio of an output power level for adesired heating cycle of operation to the second power level.
 9. Theapparatus of claim 8 wherein the power amplifier has a maximum efficientrange and the controller is configured to set the first power level tobe amplified within the maximum efficient range.
 10. The apparatus ofclaim 8 further comprising at least one sensor to measure power outputfrom the power amplifier and send a signal representative of the poweroutput to the controller wherein the controller is configured todetermine the maximum efficient range based on the power output.
 11. Theapparatus of claim 8 further comprising memory coupled with thecontroller and having a look up table with maximum efficient range forthe power amplifier.
 12. The apparatus of claim 8 wherein the controlleris further configured to determine a deep gain compression zone relativeto a compression point of the power amplifier and to set the first powerlevel to be amplified in the deep gain compression zone.
 13. Theapparatus of claim 8 wherein the controller is further configured todetermine a deep gain compression zone relative to a compression pointrelative to at least one of a maximum efficiency and to set the firstpower level, a maximum output power of the power amplifier, or a maximumgain of the power amplifier.
 14. The apparatus of claim 8 wherein thecontroller is further configured to determine a maximum power needed toheat an article in the heating device, and set the predetermined dutycycle based on the maximum power needed.